The present invention relates to an insulated-gate semiconductor device and, more particularly, to such device having low on-resistance.
Insulated-gate semiconductor devices possess the desirable feature of having a high-impedance gate, which minimizes the requirements for gate-drive circuitry. One prior art insulated-gate semiconductor device comprises an insulated-gate field-effect transistor (IGFET), a particular version of which is a metal-oxide semiconductor field-effect transistor (MOSFET). An IGFET may be of the normally-off type, wherein it cannot conduct current unless its gate is actively biased. Such normally-off device comprises a body of semiconductor material containing, in successive adjacent arrangement, a highly-doped N conductivity type (or "N.sup.+ ") source region, a moderately-doped P conductivity type (or "P") base region, a moderately-to-lightly-doped N conductivity type (or "N") drift region, and a highly-doped N conductivity type (or "N.sup.+ ") drain region. Source and drain electrodes are attached to the source and drain regions, respectively, and are adapted to be connected to external circuitry for carrying load current that flows through the device.
In the foregoing IGFET, the N drift region doping concentration is selected to be moderate to low, for example below about 10.sup.14 dopant atoms per cubic centimeter, so that the device is capable of supporting large voltages between its source and drain electrodes without becoming conductive in its forward blocking state. The low conductivity of the N drift region, however, has the undesirable consequence of increasing the on-resistance, or resistance during forward conduction, of the IGFET. This severely limits the current rating of the device.
It is an object of my invention, therefore, to provide an insulated-gate semiconductor device that is capable of supporting large forward blocking voltages and yet which has a low on-resistance.
A further object of my invention is to provide an insulated-gate semiconductor device with low on-resistance that exhibits normally-off performance.
Another object of my invention is to provide an insulated-gate semiconductor device with low on-resistance that is compact in size.
In brief summary, in accordance with a preferred embodiment of my invention, I provide an insulated-gate semiconductor device which includes an IGFET having, in successive adjacent arrangement, an N.sup.+ source region, a P base region, an N drift region, and an N.sup.+ drain region. Source and drain electrodes are attached to the N.sup.+ source and drain regions, respectively, and constitute the main current-carrying electrodes of the device. The semiconductor device further includes both a P carrier injection region adjoining the N drift region so as to form a P-N junction therewith and a bias means connected to this P carrier injection region. The bias means is effective during the on-state of the semiconductor device to forward-bias the aforementioned P-N junction by a voltage sufficient to induce injection of holes (minority current carriers) across the P-N junction, from the P carrier injection region to the N drift region. The increase in hole population in the drift region induces a like increase in the electron population in the drift region, thereby reducing the on-resistance of the drift region and the semiconductor device by several orders of magnitude.